Online solid-phase extraction coupled to liquid chromatography and tandem-mass spectrometry for the determination of glyphosate and other polar pesticide residues in plant commodities

The LC-MS/MS analysis of highly polar organophosphonate and -phosphinate pesticide residues such as glyphosate (Gly), N-acetyl-Gly, aminomethylphosphonic acid, glufosinate (Glu), N-acetyl-Glu, methylphosphinicopropionic acid, fosetyl, and ethephon remains a challenge, because matrix effects can strongly impair their determination. Here, we aimed to overcome such issues by means of an online SPE-LC-MS/MS method using ZrO₂ (zirconia) as the adsorbent for these analytes. Extracts obtained with the widely employed Quick Polar Pesticides (QuPPe) method were first directed to the ZrO₂ SPE column to trap the target analytes while the bulk of matrix compounds were removed. Initial direct linking of the ZrO₂ SPE column with the tandem mass spectrometer (MS/MS) verified a full retention of the analytes, despite the presence of competing matrix compounds present in critical matrix extracts. The trapped analytes were released in backflush mode. The use of two HPLC pumps enabled the parallel rinsing of the ZrO₂ SPE column during the separation of the analytes on the analytical HPLC column and their MS/MS quantification. Using this concept, the developed online SPE-LC-MS/MS method proved to be sensitive with moderate and generally comparable matrix effects for five plant-based commodities, including rather complex matrices such as soy flour. After successfully validating the method in accordance with Document No. SANTE/11312/2021 down to 0.01 mg/kg for each analyte, the method was applied to 172 routine samples of plant origin. Overall, the online SPE-LC-MS/MS method turned out to be a promising alternative for the analysis of highly polar organophosphonate and -phosphinate pesticide residues in complex matrices.